<%@ page contentType="image/jpeg"
         import="java.util.*,java.awt.*,java.io.*,java.awt.image.*,javax.imageio.*"
         pageEncoding="utf-8"%>
<%!Color getRandColor(int fc, int bc) {//给定范围获得随机颜色
  Random random = new Random();
  if (fc > 255)
    fc = 255;
  if (bc > 255)
    bc = 255;
  int r = fc + random.nextInt(bc - fc);
  int g = fc + random.nextInt(bc - fc);
  int b = fc + random.nextInt(bc - fc);
  return new Color(r, g, b);
}%>
<%
  //设置页面不缓存
  response.setHeader("Pragma", "No-cache");
  response.setHeader("Cache-Control", "no-cache");
  response.setDateHeader("Expires", 0);
  // 在内存中创建图象
  int width = 60, height = 20;
  BufferedImage image = new BufferedImage(width, height,
          BufferedImage.TYPE_INT_RGB);
  // 获取图形上下文
  Graphics g = image.getGraphics();
  //生成随机类
  Random random = new Random();
  // 设定背景色
  g.setColor(getRandColor(200, 250));
  g.fillRect(0, 0, width, height);
  //设定字体
  g.setFont(new Font("Times New Roman", Font.PLAIN, 18));
  //画边框
  //g.setColor(new Color());
  //g.drawRect(0,0,width-1,height-1);
  // 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到
  g.setColor(getRandColor(160, 200));
  for (int i = 0; i < 155; i++) {
    int x = random.nextInt(width);
    int y = random.nextInt(height);
    int xl = random.nextInt(12);
    int yl = random.nextInt(12);
    g.drawLine(x, y, x + xl, y + yl);
  }
  // 取随机产生的认证码(4位数字)
  String sRand = "";
  for (int i = 0; i < 4; i++) {
    String rand = String.valueOf(random.nextInt(10));
    sRand += rand;
    // 将认证码显示到图象中
    g.setColor(new Color(20 + random.nextInt(110), 20 + random
            .nextInt(110), 20 + random.nextInt(110)));// 调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
    g.drawString(rand, 13 * i + 6, 16);
  }
  // 将认证码存入SESSION
  session.setAttribute("rand", sRand);
  // 图象生效
  g.dispose();
  OutputStream output = response.getOutputStream();
  // 输出图象到页面
  ImageIO.write(image, "JPEG", response.getOutputStream());
  output.flush();
  out.clear();
  out = pageContext.pushBody();
%>